Windmills of the prior art have shown that the pitch of the blades can be changed to accommodate changes in wind velocity. Thus, when the velocity of the wind increases, it is desirable to reduce the pitch of the blade so that the strong force of the wind will not blow the structure to the ground. The German Professor Ulrich Hutter, introduced a light-weight constant-speed rotor that was controlled by variable-pitch propeller blades. However, the feathering devices of the prior art did not contemplate cyclical feathering to overcome the gyro effect or to adjust for a difference in the rotor axis and the wind direction, but were designed merely to accommodate changes of velocity of the wind.
Most types of horizontal axis rotors are yaw-active and will "track" the changing direction of the wind. Small systems are usually designed to yaw using a tail-vane whereas larger systems are normally servo operated. Reference is made to U.S. Pat. Nos. 2,353,082, and 2,484,291 which show a pilot vane for rotating the entire housing into the direction of the wind. However, the devices of the prior art did not cyclically change the pitch to operate the windmill more efficiently.
Acknowledgement is also made of the devices used for cyclical change in the pitch of blades in the auto-gyro or the helicopter art, but windmills are "passive" whereas helicopters require a tail rotor to overcome the gyro forces of the "active" blade.
The need for adjusting the pitch in the windmill is becoming increasingly critical in view of the development of two-bladed windmills. The blades of such rotors have extremely great length to take advantage of continuous but fairly light winds to utilize wind energy as a means for generating power, particularly electrical power.
In order to make maximum utilization of the wind and to provide an efficient rotor, it is necessary to keep the rotor "facing" into the wind at all times and to do this it is necessary quickly to adjust to changes in wind direction and to overcome the gyroscopic effect of the rotating blades which tends to resist the easy and automatic tuning. Pilot vanes were used in the past, coupled with manual or servo means, to turn the housing which supports the rotor and to point such housing into the wind. However, such devices are ineffective in constantly changing crosswinds.